[Bug 112072] New: DisplayPort over USB-Type C Connector Not Recognised on Intel NUC8i5BEK (Gen 9, CoffeeLake)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=112072

            Bug ID: 112072
           Summary: DisplayPort over USB-Type C Connector Not Recognised
                    on Intel NUC8i5BEK (Gen 9, CoffeeLake)
           Product: DRI
           Version: unspecified
          Hardware: x86-64 (AMD64)
                OS: Linux (All)
            Status: NEW
          Severity: normal
          Priority: not set
         Component: DRM/Intel
          Assignee: intel-gfx-bugs at lists.freedesktop.org
          Reporter: geoffrey at allott.email
        QA Contact: intel-gfx-bugs at lists.freedesktop.org
                CC: intel-gfx-bugs at lists.freedesktop.org

I am running linux kernel 5.3.1 on an Intel NUC8i5BEK which has CoffeeLake
graphics (Intel® Iris® Plus Graphics 655).

The device has two graphics output ports, 1 HDMI and 1 USB Type-C. The kernel
reports 3 connectors; port A appears to be for embedded DisplayPort which is
reported disconnected (there is a note "Haswell uses DDI functions to detect
digital outputs. On SKL pre-D0 the strap isn't connected, so we assume it's
there.").

I've connected an ASUS ROG PG278Q Monitor to the USB Type-C port using a Type-C
to DisplayPort cable, but no video modes are reported except for the default
VGA ones, meaning I'm stuck at a resolution of 1024x768. (The monitor supports
2560x1440 at 144). The video output does work, though.

I have noticed that the function `bool intel_phy_is_tc(struct drm_i915_private
*dev_priv, enum phy phy)` will always return `false` for this particular GPU
(which is GEN 9).

In `static int intel_dp_get_modes(struct drm_connector *connector)` for DP-2
(the only connected connector) there is no EDID detected, it is not eDP and
there is no fixed mode; so get_modes adds no modes.

I should note that this problem occurs both on my custom kernel and on the
latest Arch Linux ISO and the latest Ubuntu ISO. The Intel UEFI-BIOS recognises
the monitor's native resolution just fine.

Here's my kernel config:
https://pastebin.com/hStMFVfE

Here's a kernel log with drm logging enabled:
https://pastebin.com/VNhZGJPu

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